In an ATM communication network which is designed according to asynchronous transfer mode, ATM communication terminal equipment is connected to at least partially meshed ATM switching units. The physical connections between ATM switching units and between these and the ATM communication terminal equipment are divided into virtual paths and virtual channels. In a connection setup, prior to the start of the transmission of useful data, connection tables with routing information that consists of virtual channel identifiers (referenced VCI hereinafter) and virtual path identifiers (referenced VPI hereinafter) are created in the respective ATM switching units by means of an exchanging of signalling information. It is indicated by the VCI and VPI inserted into the connection tables how the virtual paths, or respectively, the virtual transmission channels which are contained in the virtual paths, of the incoming and outgoing virtual connections of the ATM switching unit are allocated to one another by the signalling. An item of routing information consisting of a VPI and a VCI is inserted in a head field in ATM cells which transport useful data and which are switched via these connections. In an ATM switching unit, the head fields of the incoming ATM cells are processed; i.e., the routing information contained there is analyzed. The ATM cells are subsequently switched to a destination, which is determined by the analyzed routing information, through the coupling network which is arranged in the ATM switching unit and which consists of one or more coupling elements.
Communication networks can also be designed as local networks (LAN). A particularly advantageous communication network for connectionless communication services is a ring network. Ring networks are usually realized according to the IEEE Standard 802.5. According to this standard, information is transmitted in the ring network serially from station to station, or respectively, from communication terminal equipment to communication terminal equipment. According to this standard, a station transmits to the ring the information to be transmitted, which information circulates in said ring from one station to the next. The relevant information is copied by the destination station that is identified by the destination address, and said information is simultaneously forwarded to the next station. When a transmitting station receives the data it originally transmitted, these are removed from the transmission medium. Ring network addresses are provided for the switching of information. According to the IEEE Standard 802.5, in a targeted transmission to one station in a destination address field, a ring network individual address is inserted, and in a targeted transmission to a predeterminable group of stations, a ring network group address is inserted. Furthermore, a tokenxe2x80x94a specific bit sequencexe2x80x94circulates in the ring network, with the aid of which token access to the ring network resources is controlled. The token is transmitted subsequent to a successfully completed information transfer and circulates via the transmission medium, i.e. is delivered from one station to the subsequent station. Stations can obtain access to the transmission medium in that they remove the circulating token. Upon the end of the data transfer, the transmitting station generates a new token so that other stations can obtain access to the transmission medium.
Furthermore, ATM communication networks in which local networks (LAN""s) are integrated are currently being designed. For example, Great Britain reference, GB 2 302 234 A teaches an ATM communication network, which is designed according to autonomous transfer mode, in which a plurality of ATM communication terminal devices can be allocated to an ATM ring network structure.
In the reference xe2x80x9cATM Internetworking, White Paper, May 1995xe2x80x9d (Anthony Alles, pp. 25-33), two methods are described for controlling a ring network access and the ring network communication according to a ring network protocol within an ATM communication network. According to a first method, also known as xe2x80x9cnative mode operationxe2x80x9d, the ring network addresses, or respectively, ring network group addresses are converted directly into ATM destination addresses by an xe2x80x9caddress resolution mechanismxe2x80x9d, and the information is transmitted via the ATM communication network. LAN emulation is cited as another method for the realization of ring network protocols in an ATM communication network. The task of an LAN emulation protocol is to emulate a local network superimposed on an ATM communication network. The emulation of an ethernet or token ring network structure takes place in centrally arranged specific units such as an LAN emulation client, an LAN emulation server, a broadcast and unknown server, or an LAN emulation configuration server. Communication requests by communication terminal equipment which is allocated to the local network LAN are switched via the ATM communication network to these central means, from which the LAN-specific handling of the communication connections is performed.
The invention is based on the object of realizing, with the lowest additional outlay, an emulated ring network structure in an ATM communication network which is designed according to asynchronous transfer mode.
In the inventive method for realizing emulated ring network structures in a communication network that is designed according to asynchronous transfer mode, a plurality of ATM communication terminal devices are connected to an ATM switching unit that is designed according to ATM. ATM cells comprising a cell head which are transferred from the ATM communication terminal devices to the ATM switching unit are switched to an ATM destination communication terminal device with the aid of routing information which respectively consists of a virtual path identifier VPI and a virtual channel identifier VCI. The ATM communication terminal devices can be allocated to a ring network structure, whereby a ring network address is assigned to these ATM communication terminal devices, respectively, and the ring network access and the ring network communication is controlled in a ring-network-specific manner. The essential aspect of the inventive method is that a virtual path is respectively set up in every transmission direction between the allocated ATM communication terminal devices and the ATM switching unit as a virtual path. In a ring network structure communication, a virtual ring network channel identifier which represents a ring network address is assigned to the virtual ring network path identifier representing the respective virtual ring network path. The ATM cells that are transmitted via the virtual ring network structure are respectively switched to the ATM communication terminal devices that are addressed by the ring network address.
An essential advantage of the inventive method is that an emulated ring network structure (LAN emulation) is realized particularly simply by setting up a virtual ring network path in a communication network that is designed according to autonomous transfer mode ATM and by imaging a ring network address identifying one or more ATM communication terminal devices into the virtual channel identification of ATM cells.
In a ring network structure that is led via a plurality of at least partially meshed ATM switching units, a virtual path which is directed according to the transmission direction of the ring structure is set up as a virtual ring network path between the relevant ATM switching units, whereby virtual ring network paths are represented by virtual ring network path identifiers. In a ring network structure communication between the ATM switching units, the ATM cells are switched to the respective established ring network paths with the aid of virtual ring network path identifiers and are transmitted via these. An emulated ring network structure, or respectively, an LAN emulation is thus advantageously realized, without additional central means (e.g. LAN server, LAN router), in an ATM communication network which comprises a plurality of ATM switching units and a plurality of ATM communication terminal devices.
The ring network address represents either a ring network individual address or a ring network group address.
According to another advantageous development, a first predetermined ring network group address represents a broadcast address and a second predetermined ring network group address represents a ring network token, whereby the ring network token controls the access to the ring network structure.
With respect to its size and to the identifier of the ring network individual address and ring network group address, the ring network address is advantageously formed according to the IEEE Specification 802.5. The ring network token is represented by a predeterminable ring network group address. Due to the standardized addressing, network applications, or respectively, network drivers that are already realized can be transferred onto the emulated ring network structure without a great outlay for adaptation.
According to another advantageous development, the ATM cells which are transmitted to an ATM switching unit and which comprise a ring network group address are switched, by means of a ring table, to the ATM communication terminal devices which are connected to the ATM switching unit and which are allocated to the ring network structure. Due to the setup of a ring table in each ATM switching unit that is allocated to the emulated ring network structure, the emulated ring network structure, or respectively, the virtual ring network path is realized with extremely little additional outlay.
Given a currently specified ring network individual address, this is converted into an ATM communication network address and switched directly to the relevant ATM communication terminal device according to the converted ATM communication network address. ATM cells comprising a ring network individual address are not switched to all the ATM communication terminal devices which are allocated to the emulated ring network structures, but are switched directly to the ATM communication terminal device represented by the ring network individual address. In the data transmission with a ring network individual address, greater security is achieved in the data transmission, since the information, or respectively, ATM cells to be transmitted are switched directly, i.e. in a connection-oriented manner and not in a connectionless manner, i.e. via every ATM communication terminal device that is connected to the emulated ring network structure.